Where can I download older versions of Blender?
Accordoing to the blender.org fortunately "Your old files are safe, every Blender release is available for download. Forever." Just go to the download site and look for previous versions at the bottom of the page.

2.79:
https://www.blender.org/download/previous-versions/

2.80:
https://download.blender.org/release/Blender2.80/

Every build:
https://download.blender.org/release/